The industrial importance and broad applicability of microporous materials (See Rouquerol, J. et al., Pure & Appl. Chem. 66, 1739-1758 (2004)) has long motivated the search for new crystalline materials exhibiting porosity or inclusion behavior. Inorganic zeolites, activated carbons and aluminum phosphates (AlPO4) play vital roles in commercial applications (separations, catalysis, ion exchange) but are limited in their synthetic variability. (See Wilson et al., J. Am. Chem. Soc. 104, 1146-1147 (1982)).
For decades, however, it has been recognized that microporous molecule based materials may be particularly advantageous as the power of molecular/organic synthetic chemistry can be brought to bear on materials-oriented synthesis. Werner clathrates (see Powell, H. M., J. Chem. Soc. 61-73 (1948); Allison, S. A. & Barrer, R. M., J. Chem. Soc. A 1717-1723 (1969)), Dianin's compound (see Dianin, A. P., J. Russ. Phys. Chem. Soc. 36, 1310-1319 (1914); Barrer, R. M.; Shanson, V. H., J. Chem. Soc. Chem. Commun. 1976, 333-334), TPP (see Allcock, H. R., J. Am. Chem. Soc. 86, 2591-2595 (1964); Allcock, H. R., et al., Inorg. Chem. 25, 41-47 (1986)) and hydrogen-bonded 3D networks (see Brunet, P., et al., J. Am. Chem. Soc. 119, 2737-2738 (1997)) to name a few, are notable examples of discrete molecule microporous materials and have been integral in establishing the contemporary field of “crystal engineering”. (See Desiraju, G. R., Angew. Chem. Int. Ed. 46, 8342-8356 (2007)).
The confluence of interest in the crystal engineering of molecular materials, porous inorganic materials, and metal-ligand self-assembly culminated in Robson's elucidation of the importance of crystalline coordination polymers (CPs) (see Robson, R., Dalton Trans. 5113-5131 (2008)) and metal-organic frameworks (MOFs) (see MacGillivray, L. Metal-Organic Frameworks: Design and Application, John Wiley & Sons, Hoboken, N.J., (2010); Long, J. R. & Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1201-1507). It also has expanded to the development of covalent organic frameworks (COFs) (Cote, A. P., et al., Porous, Crystalline, Covalent Organic Frameworks. Science 310, 1166-1170 (2005)) and polymers of intrinsic microporosity (PIMs) (McKeown, N. B. & Budd, P. M. Polymers of Intrinsic Microporosity (PIMs), Encyclopaedia of Polymer Science and Technology, John Wiley & Sons, Hoboken, N.J., (2002)) among other scaffolds.
Discrete organic molecular cages (see Tozawa, T., et al., Nat. Mater. 8, 973-978 (2009)) that are incapable of close-packing have established the importance of intrinsically porous molecules (Holst, J. R., et al., Nat. Chem. 2, 915-920 (2010)) that have applicability in selective gas separations and sorption. Also, materials that exhibit “porosity without pores” (Barbour, L. J., Chem. Commun. 1163-1168 (2006)), possess molecule-sized voids, but no molecular scale channels leading to these spaces, so permeability is based upon the ability of the small molecules to diffuse through a barrier; thus by definition, these materials are not formally porous, e.g., calix[4]arenes.
Calix[n]arenes (Gutsche, D. C., Calixarenes: An Introduction (Monographs in Supramolecular Chemistry (Royal Society of Chemistry, London, 2008)) are a class of macrocycles that have, for decades now, received attention related to their concave, bowl-like shape, which offers a cavity for the complexation of small molecules. So calix[n]arenes and their derivatives exhibit a high propensity to form inclusion compounds in the solid state due to both stabilizing host-guest interactions, and they have the general inability to form close packed structures in pure form. (Atwood, J. L., Science 296, 2367-2369 (2002)). Numerous studies on p-tert-butylcalix[4]arene helped to elucidate the nature of these materials towards gas adsorption as the t-butyl groups provide an obstacle to efficient packing. (Atwood, J. L., Science 298, 1000-1002 (2002)). The remarkable gas inclusion properties of these materials has prompted the study of calix[4]resorcinarenes, and more specifically, cavitand derivatives.
Calix[4]resorcinarenes (Hogberg, A. G. D., J. Am. Chem. Soc. 102, 6046-6050 (1980)), synthesized by an acid-catalyzed condensation of resorcinols and aldehydes, maintain their bowl-like shape through hydrogen bonding and can be further reacted to yield cavitands via intramolecular linking of the phenolic groups. (Cram, D. J., Science 219, 1177-1183 (1983)). The propensity for cavitands to incorporate a guest unit in their cavity in the solid-state is virtually guaranteed: of the 110 cavitand crystal structures reported in the Cambridge Structural Database (CSD), none contain void space in their packing.
But cavitand crystal structures containing void spaces in crystal packing could provide useful compositions for industrial applications, such as, separations, catalysis, ion exchange. It is an object of this invention to produce cavitand crystal structures with void spaces that are suitable for industrial use.